1. Field of the Invention
The invention relates to a superconducting device having a cryosystem with a cryogenic medium cooled by a refrigeration installation. The superconductors of at least one superconducting appliance and the superconducting switching path, which is electrically connected to these superconductors, of a superconducting switch are thermally coupled. The superconducting switching path has associated heating means for controlled changing of the superconducting material of the switching path to the normally conductive state.
2. Description of the Related Art
EP 0 074 030 A2 discloses a corresponding superconducting device having a cryosystem of the relevant type.
In the case of superconducting switches, the physical effect of the controllable change from the superconducting state to the normally conductive state can be used to provide a switching function, in particular in those situations in which there is no need for potential isolation directly with the actual switching process. Corresponding switches are used in particular in the field of magnetic resonance imaging (MRI) for medical diagnosis as so-called continuous current or short-circuiting switches for superconducting magnets. In order to allow current to be applied to the superconducting magnet windings of such appliances/magnets, the superconducting switching path of the short-circuiting switch which bridges them must be opened. In this case, the superconducting state can be overcome by increasing the temperature above the critical temperature, by increasing the electrical current density and/or by increasing the magnetic field on the switching path. Corresponding switching paths, which can be controlled thermally, in superconducting switches have been known for a long time (see EP 0 074 030 A2, U.S. Pat. Nos. 3,255,335 or 4,602,231).
The superconducting switch is normally located within a cryosystem having a cryogenic medium which is also used to cool the superconductors of a superconducting appliance, such as magnet winding (see the EP-A2 Document mentioned initially). This means that, when the switch is in the warm, normally conductive state, it introduces a considerable amount of heat into the cryogenic medium of the cryosystem. This amount of heat may be up to several watts in a liquid-helium (LHe) bath of an MRI magnet. In many cases, introduction of heat such as this is unacceptable. This relates in particular to recondensing, closed cryosystems, in which the refrigeration power is provided by a cold head of a refrigeration installation, for example in the form of a so-called cryocooler. Cryocoolers such as these are, in particular, of the Gifford McMahon or Stirling type, or are in the form of so called pulse-tube coolers.